1. Field
The following description relates to a current controlling mode direct current (DC)-DC converter. The following description also relates to a current controlling mode DC-DC converter that is controlled to operate in a Pulse Width Modulation (PWM) operation mode or a Pulse Frequency Modulation (PFM) operation mode depending on power consumption of a load.
2. Description of Related Art
A DC-DC converter is classified into a Pulse Width Modulation (PWM) mode and a Pulse Frequency Modulation (PFM) mode according to a controlling mode in which the DC-DC converter operates.
The PWM controlling mode is a more general mode for switch control. This mode controls a switch to be repeatedly turned on or off by being synchronized with a clock signal that has a constant cycle. Accordingly, because it is possible to stabilize output voltage to a desired voltage value, the PWM controlling mode maintains an output voltage in a large load condition. However, in the PWM controlling mode, since the switching is performed every cycle, power loss caused by the switching performed every cycle may be relatively large with respect to power consumption at an output load. Thus, when the PWM controlling mode is applied to the DC-DC converter having a small load, there is an issue that efficiency of the DC-DC converter is degraded.
Meanwhile, the PFM controlling mode is another mode that operates the switch only when needed. Thus, such a mode operates without constantly synchronizing a turned-on or turned-off state of the switch with the clock signal. Accordingly, the PFM controlling mode may improve conversion efficiency in such a DC-DC converter having a small load. However, the PFM mode presents the issue that an output ripple is relatively higher than that in the PWM controlling mode.
As stated above, the PWM controlling mode and the PFM controlling mode each have complementary strengths and weaknesses. Thus, the PWM controlling mode and the PFM controlling mode may be used together depending on a change in a load in various electronic devices in which efficiency of the DC-DC converter is a significant issue. For example, when a size of the load is divided into a heavy load and a light load, by driving the DC-DC converter in the PWM controlling mode in the heavy load and by driving in the PFM controlling mode in the light load, the DC-DC converter operates with high efficiency regardless of the load.
An example of such a DC-DC converter, illustrated in FIG. 1, includes a configuration of a DC-DC converter that has a PWM controlling mode and a PFM controlling mode and is driven in the PFM mode when a small amount of current flows in a load.
However, as shown in FIG. 1, the DC-DC converter illustrated in FIG. 1 has a configuration in which the converter is switched between operating in the PWM controlling mode and operating in the PFM controlling mode by an operation of a conversion switch based on a conversion controlling signal (CNT). In this example, there is an issue that a control signal is used to switch from one mode to the other.
As another example, there may be provided a load detecting circuit so as to control operating the DC-DC converter in the PWM operation mode or in the PFM operation mode depending on a size of the load. Thus, this example corresponds to a case in which the load detecting circuit is connected to an output terminal. However, in this case, there is an issue that the entire circuit configuration is made more complicated due to the integration of the load detecting circuit into the entire circuit.